Blood in the urine (hematuria) can make urine appear pink, red, or brown, depending on the amount of blood, how long it has been in the urine, and how acidic the urine is. An amount of blood too small to change color of the urine (microscopic hematuria) may be found by chemical tests or microscopic examination. Microscopic hematuria may be found when a urine test is done for another reason.

People with hematuria may have other symptoms such as pain in the side or back (flank), lower abdominal pain, an urgent need to urinate, or difficulty urinating, depending on the cause of blood in the urine. If sufficient blood is present in the urine, the blood may form a clot. The clot can completely block the flow of urine, causing sudden extreme pain and inability to urinate. Bleeding severe enough to cause such a clot is usually caused by an injury to the urinary tract.

Red urine is not always caused by red blood cells. Red or reddish brown discoloration may also result from the following:

Hemoglobin (which carries oxygen in red blood cells) in the urine due to the breakdown of red blood cells

Muscle protein (myoglobin) in urine due to the breakdown of muscle cells

Porphyria (a disorder caused by deficiencies of enzymes involved in the production of heme, a chemical compound that contains iron and gives blood its red color)

Causes

Blood in the urine may be caused by problems anywhere along the urinary tract from the kidneys to the ureters, bladder, or urethra. Some women at first mistake vaginal bleeding (see Vaginal Bleeding) for blood in the urine.

Common causes

The most common causes differ somewhat by the person's age but overall are

Less common causes

Disorders of the small blood vessels of the kidneys (called kidney filtering disorders or glomerular disorders)

Cysts in the kidneys (polycystic kidney disease)

Narrowing scars (called strictures) or other abnormalities of the ureters

Cancer and benign prostatic hyperplasia may cause blood in the urine. These disorders are a concern mainly in people over 50, although younger people with risk factors (smoking, family history, or chemical exposures) may develop cancer.

Disorders of the microscopic blood vessels of the kidneys (glomeruli) can be a cause at any age. Kidney filtering disorders (glomerular disorders—see see Kidney Filtering Disorders) may be part of a kidney disorder or may occur as a result of a disorder elsewhere in the body. Such disorders include infections (such as a heart valve infection), connective tissue disorders (such as systemic lupus erythematosus), blood disorders (such as serum sickness), or certain chronic disorders (such as diabetes). Also, almost any kind of kidney damage may cause small amounts of blood in the urine.

Severe injuries, such as from a fall or a motor vehicle crash, can injure the kidneys or bladder and cause bleeding.

Schistosoma haematobium, a parasitic worm that causes disease in Africa and, to a lesser extent, in India and parts of the Middle East, can invade the urinary tract, causing blood in the urine. Doctors consider schistosomiasis only if people have spent time in areas where the worm is found. Tuberculosis may cause blood in the urine.

Evaluation

Doctors first try to establish that bleeding is the cause of red urine. Then they look for the cause of the bleeding, including where in the urinary tract (or occasionally elsewhere) the bleeding is originating. The following information can help people know when to see a doctor and what to expect during the evaluation.

Warning signs

In people with blood in the urine, certain symptoms and characteristics are cause for concern. They include

Large amount of blood in the urine

Age over 50

Swelling of the feet or legs, plus high blood pressure

When to see a doctor

People who notice blood in their urine should see their doctor within a day or two. However, people who are passing a large amount of blood, who are unable to urinate, or who have severe pain should see a doctor right away.

What the doctor does

Doctors first ask questions about the person's symptoms and medical history and then do a physical examination. What they find during the history and physical examination often suggests a cause of the blood in the urine and the tests that may need to be done (see Table: Some Causes and Features of Blood in the Urine).

Doctors ask how long blood has been present and whether there have been any previous bleeding episodes. They ask about symptoms of urinary blockage, such as difficulty starting urination or inability to completely empty the bladder. Pain or discomfort is an important finding. Burning during urination or dull pain in the lower abdomen just above the pubic bone suggests a bladder infection. In men, mild to moderate pain in the lower back or pelvis is often the result of a prostate infection. Extremely severe pain is usually due to a stone or a blood clot blocking the flow of urine.

Doctors then do a physical examination. Usually, a pelvic examination is necessary in women. If women have blood in the vagina, a catheter may need to be inserted into the bladder to see whether the source of blood is the bladder or the vagina. In men, doctors usually do a digital rectal examination to check the prostate.

Testing

Sometimes doctors can make a diagnosis based on the person's symptoms and the results of the physical examination. More often, because symptoms of many disorders overlap, testing is needed to determine the cause (or sometimes the presence) of blood in the urine. Urinalysis is the first test done. Urinalysis can detect blood (confirming that the red color of the urine is caused by blood) and may show evidence of a kidney filtering disorder. If infection is suspected, urine culture is usually done.

In all people over 50 and in people who have risk factors for cancer, doctors typically use a flexible viewing tube to look inside the bladder (cystoscopy) to determine the cause of bleeding.

People of any age who do not have an infection or a kidney filtering disorder as the cause of visibly bloody urine typically have imaging studies, such as computed tomography (CT), ultrasonography, or magnetic resonance imaging (MRI) of the abdomen and pelvis. For people under 50 who have only microscopic hematuria and no other abnormalities detected during the physical examination, blood tests, or urinalysis, doctors may simply repeat the urinalysis in 6 or 12 months. If blood is still present, they will do further tests.

If doctors suspect a kidney filtering disorder (based of the results of urinalysis), they usually do blood tests to evaluate kidney function and sometimes a kidney biopsy. Blood tests for sickle cell disease may be needed in people of African or Mediterranean descent who are not known to have the disease.

In men who are 50 or older, doctors usually measure the level of prostate specific antigen (PSA) in the blood.

Treatment

Treatment is directed at the cause of the bleeding. Whatever the cause, if urine flow is blocked by blood clots, doctors usually insert a flexible tube in the bladder (urinary catheter) and try to flush out the blood clot.

Key Points

Red urine is not always caused by blood.

Many causes of blood in the urine are not serious.

Risk of serious disease increases with age and the duration of the bloody urine.

Testing for cancer is usually needed only for people over 50 or for younger people with risk factors for cancer.

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